This invention relates to lubricant compositions, and more particularly to lubricant compositions containing a synergistic mixture of a hydrocarbyl-substituted mono and bis succinimide having polyamine chain linked hydroxacyl radicals and a neopentyl polyol derivative as a detergent and/or dispersant.
Internal combustion engines operate under a wide range of temperatures including low temperature, stop and go service as well as high temperature conditions produced by continuous high speed driving. Stop-and-go driving, particularly during cold, damp weather conditions, leads to the formation of a sludge in the crankcase and in the oil passages of a gasoline or a diesel engine. This sludge seriously limits the ability of the crankcase oil to lubricate the engine. In addition, the sludge with its enrapped water tends to contribute to rust formation in the engine. The noted problems tend to be compounded by standard lubrication service recommendations for extended oil drain intervals. With the introduction of four cylinder internal combustion engines which must operate at high speeds to produce the required torque output, it has become increasingly difficult to provide a satisfactory dispersant lubricating oil composition.
The high temperature operating conditions increase the oil's propensity for oxidation. Oxidized oil thickens when cooled and will not afford satisfactory lubrication. Certain mineral oil based stocks are more prone to oxidation than others. The base stocks used in many European lubricating oils have been found to have a higher propensity for oxidation than base stocks used in the United States. Further, lubricant compositions need to be compatible with the elastomer seals used in internal combustion engines, such as Viton seals. Many oil additives have been found to be aggressive towards the seals causing their deterioration.
Previously, nitrogen containing compounds which act as dispersants and/or detergents have been used in the formulation of lubricant compositions. Many of these dispersant and/or detergent compounds are based on the reaction of an alkenylsuccinic acid anhydride with amine or polyamine to produce an alkylsuccinimide or an alkylsuccinic acid as determined by the conditions of reaction. Such products contain a high level of nitrogen in order to provide improve dispersency in a crank case lubricant composition. One such class of compounds which are excellent dispersants and/or detergents is set forth in coassigned U.S. Pat. No. 4,482,464, whose disclosure is incorporated herein by reference.
Other useful detergent and/or dispersant additives for a lubricant composition are based on derivatives of neopentyl polyols and polyolefinic-P.sub.2 S.sub.5 products. A preferred class of such compounds are set forth coassigned U.S. Pat. No. 3,281,359 whose disclosure is incorporated herein by reference. However, it is been found that with many lubricating oils particularly those containing European base stocks neither of these two class of detergents and/or dispersants have been found to be entirely satisfactory under all operating conditions.